Okay guy's heres the deal.

I'm working in a third floor basement ( Yup this building has 3 floors to its basement, I'm 30' below ground )

They have a 8 cylinder engine that runs off natural gas that is used to run the chiller for air conditioning.

When I went to look at the job they had a cover patching a hole in the muffler, they removed it prior to me getting there to look at the job.

So I looked up and seen where it had rusted through leading me to believe it was regular steel, so we rolled up a patch for the 12-1/4" diameter muffler that went 1/2 way around the pipe x 28" long.

However, Prior to starting to weld I verified with a magnet to make sure it was steel just to discover it was stainless.

So I then go back to the shop and roll some stainless that goes way outside the damaged area and weld it in and it welds up beautifull, until it cracks from the edge of the weld into the old.

( Now I've repaired stainless steam tables that burn out because they forget to keep water in them and the flame just cooks a hole which turns the stainless black and makes it unable to weld )

Thats not the case here the stainless is not blackened.

I have 2 choices left, Fabricate a new muffler or put a patch on the top side to match the one on the bottom and then all I have to worry about is wheather it will crack at each end.

Keep in mind this exhaust ties into several others and is well over 100' long.